Various types of data storage devices store digital data in magnetic or optical form on a rotating storage medium. Modern magnetic disc drives, for example, comprise one or more rigid discs that are coated with a magnetizable medium and mounted on the hub of a spindle motor for rotation at a constant high speed. Information is stored on the discs in a plurality of concentric circular tracks typically by an array of transducers (“heads”) mounted to a rotary actuator for movement of the heads substantially radially relative to the discs. Each of the concentric tracks is generally divided into a plurality of separately addressable data sectors. The read/write transducer, e.g. a magneto-resistive read/inductive write head, is used to transfer data between a desired track and an external environment. During a write operation, data is written onto the disc track and during a read operation the magneto-resistive read element of the head senses the data previously written on the disc track and transfers the information to the external environment.
The spindle motor typically includes a stator, a rotor and a spindle or shaft. The rotor may alternatively rotate with the shaft or the shaft may be stationary so that the rotor rotates about the shaft. Within a data storage device, the rotor includes a hub for supporting one or more of the data storage discs. During idle periods when the data storage device is neither reading nor writing data to the disc, the stator continuously energizes the rotor to overcome wind resistance as well as friction in the bearings as the rotor spins at high speed. Typical spindle motor speeds include 4,200 revolutions per minute and beyond.
The rotor of the spindle motor may be supported by a hydrodynamic fluid bearing. These bearings have proven useful in reducing wear in the spindle, reducing power consumption of the spindle motor and reducing vibration from the spindle motor compared to ball bearings. However, hydrodynamic bearings are susceptible to failure due to loss of hydrodynamic stiffness resulting from gas being trapped in the fluid of the bearing.
During operation, the spindle motor naturally draws in or ingests gas from the surrounding environment in the data storage device. Some of this gas is forced into the fluid of the hydrodynamic bearing. When the spindle motor is operated for an extended period of time, in some cases many days, the gas forced into the fluid of the hydrodynamic bearing can accumulate to the point at which it displaces the fluid in certain areas of the bearing resulting in a loss of hydrodynamic stiffness and part contact wear. This can cause the motor bearing components to wear and eventually fail. Accordingly there is a need for a method and apparatus for counteracting gas ingestion in a hydrodynamic bearing spindle motor. The present invention provides a solution to this and other problems, and offers other advantages over the prior art.